Replacement order

Can someone guide me on the subject stated above... Amazon have delivered for me to my customer. the customer contacted me and requested for the same product but in another color. i offered him replacement.

now the first thing I need to ask is,

will Amazon need another tracking ID for shipping the order to the customer or I can use the same tracking label.??

second this is, will amazon charge shipping charges again...? coz as per policy the Amazon give free shipping if you have item in stock...? but I am confused about that..